Andaman tribes may've a new human ancestor
Subodh Varma
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Indian-Spanish Study Says Jarawas, Onges Evolved From 3rd Branch Other Than Neanderthals & Denisovans
Two tribal communities of the Andaman Is lands, Jarawas and Onges, may have evolved from an as yet unknown human ancestor, according to latest genetic analysis done by a joint team of Indian and Spanish scientists. This claim, although not yet backed by any fossil evidence, is sensational for it will add a new, unknown branch to human ancestry.Scientists at the National Institute of Bio-Medical Genetics (NIBMG), Kalyani, West Bengal, working with those from the Pompeu Fabra University , Barcelona, Spain made this discovery after analysing ten genetic samples derived from Jarawas and Onges in the Andamans along with 60 samples drawn from different ethnic groups across India. The study has been published in the scientific jo urnal Nature Genetics.
Why is this claim of a new ancestor startling? From what is known of human evolution, an ancestor of modern humans arose in Africa and migrated west towards Europe and east towards China and India about 400,000 years ago.Those that went west evolved into the Neanderthals while those that migrated east formed the Denisovans.
Meanwhile, ancestral humans continued to evolve in Africa and about 50,000 years ago modern humans too started spreading out of Africa. As they spread to all corners of the world, they encountered earlier species like Neanderthals and Denisovans and interbred with them. All this shuffled up the genomes considerably but modern technology can tease out the intermingling. This is what the research team has done.
“In addition to the Neanderthal and the Denisovan, an extinct hominid also contributed to the ancestry of the Jarawas and the Onges,“ Partha Majumder, NIBMG director and a co-author of the research told TOI.
Earlier research by different scientists has shown that most people outside Africa ha ve 1-4% of their genetic material derived from Neanderthals, except in communities in Pacific Islands and Australian aborigines, which instead have up to 6% genetic contribution from Denisovans.
But the new discovery is being questioned by other genetic historians. Harvard professor David Reich, one of the lea ding scientists in the field who has also researched Indian genomes, told TOI that the new ancestor theory of Majumder and his team is “unlikely to be correct“, attributing the error to statistical methods. “When we and others have computed similar statistics, we obtained results that are statistically inconsistent with Mondal (the lead author) and colleagues, and that do not require the surprising hypothesis of new archaic admixture,“ he said.
But there are other aspects of the NIBMG's research that are new and free of controversy. They have established that the Andamanese are closer to Indians in their genetic makeup and likely came in the same wave of migration from Africa as others in the region.They also found that the short stature of the Jarawas and Onges is likely due to natural selection and not just because their founders were short.
Why is this claim of a new ancestor startling? From what is known of human evolution, an ancestor of modern humans arose in Africa and migrated west towards Europe and east towards China and India about 400,000 years ago.Those that went west evolved into the Neanderthals while those that migrated east formed the Denisovans.
Meanwhile, ancestral humans continued to evolve in Africa and about 50,000 years ago modern humans too started spreading out of Africa. As they spread to all corners of the world, they encountered earlier species like Neanderthals and Denisovans and interbred with them. All this shuffled up the genomes considerably but modern technology can tease out the intermingling. This is what the research team has done.
“In addition to the Neanderthal and the Denisovan, an extinct hominid also contributed to the ancestry of the Jarawas and the Onges,“ Partha Majumder, NIBMG director and a co-author of the research told TOI.
Earlier research by different scientists has shown that most people outside Africa ha ve 1-4% of their genetic material derived from Neanderthals, except in communities in Pacific Islands and Australian aborigines, which instead have up to 6% genetic contribution from Denisovans.
But the new discovery is being questioned by other genetic historians. Harvard professor David Reich, one of the lea ding scientists in the field who has also researched Indian genomes, told TOI that the new ancestor theory of Majumder and his team is “unlikely to be correct“, attributing the error to statistical methods. “When we and others have computed similar statistics, we obtained results that are statistically inconsistent with Mondal (the lead author) and colleagues, and that do not require the surprising hypothesis of new archaic admixture,“ he said.
But there are other aspects of the NIBMG's research that are new and free of controversy. They have established that the Andamanese are closer to Indians in their genetic makeup and likely came in the same wave of migration from Africa as others in the region.They also found that the short stature of the Jarawas and Onges is likely due to natural selection and not just because their founders were short.
Source: Times of India, 27-07-2016
